Method of making fitting joint for double containment pipe

ABSTRACT

A double containment pipe fitting and method of making same is disclosed. The fitting includes a branch double containment pipe section butt welded to a double containment pipe header, or main section to form a fitting wherein the branch section extends away from the header section. The header and branch section primary and secondary pipe portions contain distinct engagement surfaces which are joined together to form the fitting. A unique, non-planar heating element having opposed heating surfaces is brought into contact with the main and branch pipe sections to soften the plastic for welding purposes which are then joined together in a manner such that the respective centerlines of each pipe section intersect.

This application is a divisional application of application Ser. No.08/152,849, filed Nov. 15, 1993 now U.S. Pat. No. 5,624,140.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates generally to a new and improved pipefitting and method for making same, and more particularly, to aprefabricated, butt-welded double containment pipe fitting.

There is an ever increasing concern today over the environment andparticularly to chemical spills and leaks where chemicals are absorbedby the ground and migrate to groundwater. The cleanup of such chemicalspills is both costly and tedious. In order to provide some measure ofassurance against chemical contamination, the chemical industry,especially the chemical waste processing industry, has adopted the useof double containment pipe and underground storage tanks to convey andstore fluid chemicals.

Double containment piping consists of two pipes. Both pipes aretypically made of a thermoplastic material because of the high corrosionresistance, low weight and low cost of plastics in general. One pipe ofthe two pipes is known as the primary pipe and is intended to conveychemical fluids or effluents. The other pipe is known as a secondarypipe and it extends around the primary pipe in a spaced-apartrelationship to define an annular space between the primary andsecondary pipes.

The secondary pipe provides a protective casing or containment whichwill contain chemicals escaping from the primary pipe due to leakage andprevent the chemicals from escaping into the environment. Leak detectionor monitoring systems may be disposed within the annular space foridentifying leaks to the system processing operator.

Prior double containment piping systems were costly and labor-intensive.Double containment piping systems typically required the installationcontractor to fabricate much of the system during its installation. Thisfabrication typically included the fabrication of various fittings suchas wye, lateral, tee and reducing fittings. Certain other fittings alsowere field-fabricated such as elbows and cross fittings. This fieldfabrication was a costly aspect to any double containment piping systeminstallation. The field fabrication of such fittings was expensivebecause it required cutting pipe lengths, or spools to obtain varioussize pipe portions which were then fillet welded together using athermoplastic welding rod. This process is both time consuming to thecontractor and the owner and the quality effected in the field may notbe up to the standards of quality that can be readily replicated in afactory situation.

Although some past methods have been known for joining togetherthermoplastic pipe sections, each method has certain disadvantages. Forexample, U.S. Pat. No. 3,013,925 issued Apr. 3, 1959 describes a methodin which two pipe spools are held together in a vise and their opposingends are brought into contact with a planar heating element to melt theendwalls of the pipe sections. After heating, the pipe endwalls werebrought together and held in place until the plastic cools. This methodis only effective for joining straight pipe lengths.

U.S. Pat. No. 4,779,652, issued Oct. 25, 1988, describes a integrallymolded pipe fitting which primary and secondary pipes are moldedtogether as one piece and are separate by integral pipe supports moldedintegrally therewith. Molding the primary and secondary pipe together asa single unit requires a costly investment in molds and this investmentmay limit the ability of the pipe supplier to supply prefabricatedcustom fittings in accordance with a contractor's installation drawings.A mold must be made for each particular style fitting and therebyreduces the likelihood of a cost effective custom fitting being madequickly.

U.S. Pat. No. 5,185,049 which issued Feb. 9, 1993, describes anapparatus for butt-welding double containment pipe sections together bybringing opposing endwalls of the pipes in contact with a hinged planarheating element until the plastic softens, at which time the ends arejoined together to form a solid butt-joint. The planar nature of thisheating element precludes its use for assembly of complex fittings suchas tee, wye, cross or reducing fittings which require detailedcalculation of angled mating surfaces.

In order to reduce the amount of labor expended in construction ofdouble containment pipe systems and thereby lower the overall cost tothe system a need therefore exists for prefabricated pipe fittings,wherein the pipe fittings components are butt-welded together, therebypermitting complex fittings to be fabricated as modular components ofeither standard size or custom size of an overall double containmentpiping system.

SUMMARY OF THE INVENTION

The present invention is therefore directed to a prefabricated doublecontainment pipe fitting and to a method, or a process, for fabricatingdouble containment pipe fittings of higher structural integrity and toeliminate the need for costly field fabrication.

One principal aspect of the present invention accomplishes its intendedpurposes by providing a double containment pipe fitting in which theprimary and secondary pipe portions of a double containment main pipespool are butt-welded to opposing primary and secondary pipe portions ofa double containment branch pipe spool simultaneously while a reliablebutt-welded joint is effected where the opposing primary and secondarypipe portions of the main and branch pipe spools meet.

In another principal aspect of the present invention, a plastic firstdouble containment pipe spool is joined to a plastic second doublecontainment pipe spool at a specified angle from the longitudinal axisof the second double containment pipe spool by simultaneously contactingopposing faces of the first and second double containment spools to aheating assembly with opposing non-planar heating surfaces which arecomplementary to the opposing faces of the two pipe spools until theplastic melts, at which time the pipes are then pushed together and heldin place until the plastic hardens to simultaneously create two distinctbutt-welds one between the two primary pipe portions and the twosecondary pipe portions of the respective first and second pipe spools.

In yet another principal aspect of the present invention, a doublecontainment pipe reducing fitting comprises a main double containmentpipe section having a reduced diameter branch double containment pipesection butt-welded to the main pipe section in which the endfaces ofthe branch section are cut at an angle and brought against a heatingassembly male heating element while openings are cut in the main pipesection and then brought against a heating assembly female heatingelement located on the opposite side from the male heating element.These opposed male and female heating surfaces soften the plastic of themain and branch pipe section so as to permit them to be joined togetherto form the fitting.

In yet another principal aspect of the present invention, a method forfabricating a double containment pipe fitting includes providing aheating element having non-planar, opposed heating surfaces, cutting theedges of a first length of double containment pipe at a predeterminedangle, cutting an opening in a second length of double containment pipewhich is complementary to that of the first length, contacting the firstand second pipe lengths against an angled heating element to soften thecontact faces of the pipe plates lengths, joining the contact facestogether and holding them together until the plastic solidifies.

Accordingly, it is an object of the present invention to provide aunique double containment fitting which can be easily fabricated in afactory to any desired field dimension so that the fitting can be usedas a modular component 10, an overall double containment pipe system.

Another object of the present invention is to provide a method forassembly of a double containment pipe fitting wherein opposing contactfaces are formed in two double containment pipe lengths, each pipelength having an inner primary pipe surrounded by an outer, secondarypipe in a spaced-apart relationship, and wherein a non-planar heatingassembly is provided having opposed heating surfaces is moved intocontact with the opposing contact faces, the opposing contact faces thenbeing brought into the contact with the opposed heating surfaces andsubsequently contacted together with each other.

Still another object of the present invention is to provide athermoplastic double containment pipe fitting in which a branch fittingsection is butt-welded to a header fitting section, each of the headerand branch fitting sections having primary and secondary pipe portions,each of the header and branch fitting sections further having twodistinct engagement surfaces defined along the primary and secondarypipe portions thereof, the header and branch fitting sections beingbutt-welded together along the header and branch fitting sectionengagement surfaces.

Yet another object of the present invention is to provide a unique,non-planar heating assembly for simultaneously heating endfaces ofprimary and secondary pipe portions of double containment pipe sectionssuch that when their endfaces have softened to welding temperature, theendfaces of adjacent primary and secondary pipe sections can be joinedtogether at an angle.

These and other features, objects and advantages of the presentinvention will become apparent from a reading of the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of the following detailed description, reference will bemade to the attached drawings wherein like reference numerals identifylike parts and wherein:

FIG. 1 is perspective view of a double containment pipe fittingconstructed in accordance with the present invention;

FIG. 2 is an exploded view of the fitting of FIG. 1 showing theindividual components thereof;

FIG. 3 is a cross-sectional view of the fitting of FIG. 1 taken alonglines 3—3 thereof;

FIG. 4 is a perspective view of an apparatus used in fabricatingfittings of the present invention;

FIG. 4A is a diagrammatic plan view of the apparatus of FIG. 4 showingthe relative alignment of the two pipe sections and heating assemblyprior to joining the pipe sections together;

FIG. 4B is a diagrammatic plan view of the apparatus of FIG. 4 showingthe relative alignment of the two pipe sections after joining themtogether;

FIG. 5 is a perspective of a heating assembly used in the apparatus ofFIG. 4 to produce fittings similar to that illustrated in FIG. 1;

FIG. 6 is a perspective view of another embodiment of a fittingconstructed in accordance with the present invention, illustrating adouble containment reducing fitting;

FIG. 7 is a simplified plan view of the formation of the reducingfitting of FIG. 6;

FIG. 8A is a perspective view of one heating surface of the heatingassembly illustrated in FIG. 7 showing the male heating element used inthe assembly of the fitting of FIG. 6;

FIG. 8B is a perspective view of the opposite side of the heatingassembly illustrated in FIG. 8A, showing a female heating element usedin the assembly of the fitting of FIG. 6;

FIG. 9 is a cross-sectional view of the heating element of FIG. 7 takenalong lines 9—9 thereof;

FIG. 10 is a diagrammatic view of the components which make up thefitting of FIG. 1, illustrating the planes defined by the engagementsurface; and,

FIG. 11 is a perspective view of another fitting constructed inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a double containment pipe fitting 10 constructed inaccordance with the principles of the present invention. The fitting 10shown may be referred to in the piping art as either a “wye” or“lateral” fitting where one portion of the fitting extends away from theother portion at a specific angle. The fitting 10 is intended for use indouble containment piping systems wherein pipe lengths and fittingsinclude an inner pipe 12 located within an outer, secondary pipe 14. Thefitting 10 as with most double containment pipe systems, is formed froma thermoplastic material which offers low cost, lightweight andpreferred corrosion resistance characteristics. Polypropylene is anexample of a preferred thermoplastic material for fabricating fittingsof the present invention. Other examples of suitable thermoplastics arepolyethylene, polyvinylchloride, polyvinylidenefluoride and halar.Additionally, the fittings of the present invention may be manufacturedfrom dissimilar materials, i.e., the primary pipe 12 may be formed fromone thermoplastic material while the secondary pipe 14 may be formedfrom another thermoplastic material or vice-versa.

In double containment pipe systems, the primary pipe 12 may be heldinside of the secondary pipe 14 in a spaced-apart relationship from thesecondary pipe 14 by one or more supports, shown as anchor plates 16.The anchor plates 16 are generally planar members 18 having a circularconfiguration. The anchor plates 16 include an opening 20 disposed intheir central portion which receives therethrough either a portion ofthe primary pipe 12 or a pipe coupling 22 used for joining the primarypipe portions of adjacent double containment pipe lengths together. Theanchor plate 16 may be welded to the primary pipe 12 in a conventionalmanner such as by a fillet weld 24 using thermoplastic welding rod. Inorder to resist thermal movement of a primary pipe 12, the end portions26 of the secondary pipe portions 14 may be counterbored to define ashoulder portion 28 on the inner surface of the secondary pipe portions14. The shoulder 28 may extend circumferentially around the innersurface as shown in FIG. 3, or the shoulder may include separateportions present only at selected locations on the inner surface. Theanchor plates 16 abut against the shoulder 28. The anchor plate 16 mayfurther be preferably welded to the secondary pipes 14 at one sidethereof also by fillet welds 30. Although the anchor plates 16 have beendescribed as welded in place by means of fillet welds, it will beunderstood that other plastic welding techniques can be used such asextrusion welding and ultrasonic welding and also the use of “self”welding plastics which can be welded by applications of heat thereto.

As previously described, the fitting 10 shown in FIGS. 1-3 is a lateral,or wye fitting, and includes a two distinct pipe sections, 32, 34. Thesedouble containment pipe sections 32, 34 may be referred to in the artand in this specification as “pipe lengths” or “pipe spools”. Onesection is the “main” double containment pipe section 32 which may bereferred to in the art as a “header” section which has a longitudinalaxis L_(M) and the other section is referred to as a “branch” sectionbecause it extends, or “branches” away from the main section 32 at apredetermined angle, θ. This angle θ, is the angle between the mainsection longitudinal axis L_(M) and the longitudinal axis L_(B) of thebranch section 34. This angle θ is equal to 45° in the fitting 10 ofFIG. 1. When the fitting 10 is assembled, the branch sectionlongitudinal axis L_(B) intersects with the main section longitudinalaxis L_(M).

In an important aspect of the present invention, the header and branchpipe sections 32, 34 are joined together by way of a butt-weld 35 alonga joint 36 which extends along both the primary and secondary pipeportions 12, 14 of each pipe section. As shown in FIG. 2, a notch-likeopening 37 is cut into the main pipe section 32 and extends through bothof the primary and secondary pipe portions 12, 14 of the main pipesection 32. This opening 37 defines a engagement surface 38 of the mainpipe section 32 which has two opposing portions 38′, 38″ which intersectalong a line 40 that preferably falls within a plane passing through themain pipe section longitudinal axis L_(M). This line occurs at what maybe considered as the vertex 41 of the main pipe section opening 37.

FIG. 10 is a diagrammatic view of an exploded fitting which illustrateshow the opposing portions 38′, 38″ may be aptly characterized asdefining opposing planes P₁, P₂ which extend along endfaces 39′, 39″ &40′, 40″ of the primary and secondary pipe portions 12, 14 exposed bythe opening 37. The planes P₁, P₂ are shown in FIG. 10 as shaded whilethe area of the planes within the endfaces 39′, 39″ & 40′, 40″ are leftunshaded. In viewing these planes P₁, P₂ it can be confirmed that theengagement surface opposing portions 38′, 38″ each define approximatelyone-half of an ellipse (an ellipse being formed whenever a section istaken at an angle through a cylinder) inasmuch as their associatedplanes P₁, P₂ intersect the main pipe section longitudinal axis L_(M) atany angle which are approximately greater than 1°, approximately lessthan 180° or not equal to 90°, Were the plane defined by any opposingportion 38′, 38″ to intersect the main pipe section longitudinal axisL_(M), the plane would have a semi-circular configuration having aradius equal to that of the main pipe section secondary pipe 14.

The branch section 34 has a similar bifurcated engagement surface 48extending though its primary and secondary pipe portions 12, 14 whichcomprises two opposing portions 48′, 48″ which intersect along a line 50that preferably falls within a plane passing through the branch sectionlongitudinal axis L_(B). This line occurs at what may be considered asthe vertex 51 of the branch pipe section 34. The branch sectionengagement surface opposing portions 48′, 48″ also define opposingplanes P₁₁ P₁₂ which are offset from each other. Because these planespass through the branch section longitudinal axis L_(B) at an angle(excluding 90°), they also define partially elliptical profiles whichare complementary to those presented by the main pipe section engagementsurface opposing portions.

During assembly of the fitting 10, the main pipe section engagementsurface 38 and the branch section engagement surface 48 are brought intocontact with a heating assembly 120 until the surfaces reach apredetermined welding temperature. The two pipe lengths 32, 34 are thensubsequently brought together and held together until the plastichardens and an effective simultaneous butt-weld is formed between thetwo pipe lengths.

FIG. 4 illustrates an apparatus 100 which is particularly suited forfabricating fittings of the present invention. The apparatus 100includes a frame 102 which slidably supports two carriage members 104,106. These carriage members 104, 106 are slidable along a centerline Cof the frame 102 and are aligned therewith. The carriage members 104,106 are powered by. an appropriate means, such as hydraulic or pneumaticcylinders which moves them along the centerline, such as along rails108, toward each other. A suitable control means is provided forcontrolling the rate of movement of the carriage members 104, 106.

Each carriage member 104, 106 has a means for supporting doublecontainment pipe sections 32, 34, shown as support blocks 110, 112. Eachsupport block 110, 112 includes an arcuate support surface 114 whichcorresponds to the outer diameter of the secondary pipes 14 of the pipesections 32, 34. The pipe sections 32, 34 may be held in place withinthe support blocks 110, 112 by any suitable clamping means, such as theadjustable belt clamps 116 illustrated. The primary pipe portions 12 maybe firmly supported in the secondary pipes 14′ by anchor platesdescribed above, or they may be temporarily supported and placed byanchor plates (not shown) which are not welded to the primary andsecondary pipes.

The apparatus 100 further includes a heating assembly 120 (shown inplace within the apparatus 100 in FIG. 4 and separately in FIG. 5)having a generally non-planar configuration with two heating surfaces,or elements, 122, 123 located on opposite sides of the heating assembly120. One such surface 122 is intended to contact the main pipe section32 and its associated engagement surface 38 and its associated opposingportions 38′, 38″ and presents an exterior, or outwardly facing, angleθ_(EXT) on its heating surface 122. The other surface 123 is intendedfor contact with the branch pipe section engagement surface 48 and itsopposing portions 48′, 48″ and presents an interior, or inwardly facing,angle θ_(INT) on its heating surface 123. These angles are best shown inFIGS. 4A & 5.

The heating assembly 120 is preferably mounted to the apparatus 100 bymeans of a pivot arm 136 which may be swung in and out of place betweenthe opposing pipe sections 32, 34 mounted on the apparatus 100. In orderto serve its intended purpose of softening, or melting, the engagementsurfaces 38, 48 of opposing pipe sections 32, 34, the heating assembly120 contains conventional heating coils (not shown) which are disposedin an internal cavity or cavities of the assembly 120 and which areenergized by electrical wires 130 and transfer heat to the heatingsurfaces 122, 123 of the assembly 120. The assembly 120 may be formed byway of casting, or it may be machined from various components and boltedtogether. In the latter case, and as shown in FIG. 5, the assembly 120may be built up itself from two separate planar elements 133, 134 toform its final non-planar configuration. The heating assembly 120 ispreferably rotatably mounted to the apparatus 100 by means of a shaft132 which permits the operator to adjust the orientation of the oppositeheating surfaces 122, 123 such that they are generally parallel to theopposing portions 38′, 38″ & 48′, 48″ of the main and branch pipesection engagement surfaces 38, 48.

In operation, the respective engagement surfaces 38, 48 are formed inthe header and branch sections 32, 34 and the pipe sections 32, 34 areplaced in the support blocks 110, 112 of the carriages 104, 106 suchthat their respective longitudinal axes L_(M) and L_(B) are positionedat the intended branch angle, θ on the apparatus 100. The heatingassembly 120 is energized and when the proper welding temperature isattained, the opposing header and branch pipe sections 32, 34 are thenbrought into contact with the heating assembly opposed surfaces 122, 124and held against them until the engagement surfaces 38, 48 reach adesired thermoplastic welding temperature where the plastic begins tosoften. The two pipe sections 32, 34 and the carriage members 104, 106are then moved away from each other.

The heating element 120 is then swung out of contact with the two pipesections 32, 34 and the carriage members 104, 106 are subsequently movedtoward each other until the engagement surfaces 38, 48 thereof contacteach other. Pressure is exerted by the carriages 104, 106 on the joinedpipe sections 32, 34 to maintain them in abutting contact until thetemperature of the plastic drops below the fusion temperature and coolsto form a butt-welded joint. When the joint 36 has solidified, the pipesections are released from the clamps 116 and may be appropriatelyfinished, such as rod welding the anchor plates 16 to the secondary andprimary pipe portions 12, 14 of the fitting 10 or attaching one or morecouplings 22 to the fitting 10.

Turning now to FIG. 6, another embodiment of a fitting 200 in accordancewith the principles of the present invention is illustrated having theform of a reducing fitting 200. In the reducing fitting 200, the mainpipe section 202 has primary and secondary pipe portions 204, 206 whichhave respective pipe diameters D₁ and D₂ as shown. The branch pipesection 208 also has primary and secondary pipe portions 210, 212 whichhave respective pipe diameters d₁ & d₂. The diameters d₁ & d₂, of thebranch pipe section 208 are different from (shown in FIG. 4 as lessthan) diameters, D₁ & D₂. Typically, in a reducing fitting, the diameterof the branch section pipe portion 210 will be reduced compared to thediameter of the main section primary pipe portion 204.

The assembly of reducing fittings is carried out in a similar manner asfor regular fittings in that the main and branch sections are contactedagainst a non-planar heating assembly. Referring to FIG. 7, the main andbranch pipe sections 202, 208 are prepared by cutting openings 214 inthe primary and secondary pipe portions 204, 206 thereof. Preferably,these openings 214 are of an oval configuration. These main and branchpipe sections 202, 208 are contacted against a non-planar heatingassembly 220 having opposite heating surfaces 222, 224. As best shown inFIG. 9, the surface 222 which is brought into contact with the main pipesection 202 has a “female” element assembly 230 attached thereto. Thisfemale heating element 230 is best characterized as defining twodistinct saddle-like members 231, 232 presenting an open cavity whenviewed in profile and which combined, provide a heated surface whichsurrounds the main pipe section primary and secondary pipe portions 204,206 and heats the areas 234, 235 of those pipe portions which surroundthe openings 214. These two areas 234, 235, serve as engagement surfaces238 of the main pipe section 202.

Similarly, the opposite heating surface 224 of the heating assembly 220has a non-planar “male” heating element assembly 240 which protrude awayfrom the heating assembly baseplate 221. The male heating element 240 isgenerally complementary in its exterior configuration to the interiorconfiguration of the female heating element 230 has two distinct members241, 242 which provide a heated member which contacts the branch sectionprimary and secondary pipe portions 210, 212 and heats the endfaces 244,245 thereof. These endfaces 244, 245 serve. as the branch pipe sectionengagement surfaces 248 which are complementary to and which oppose theengagement surfaces 234, 235 of the main pipe section 202.

Lastly, FIG. 11 illustrates another embodiment of a fitting 300constructed in accordance with the present invention wherein the mainpipe section 302 has a branch pipe section 304 extending away from sameat a branch angle of approximately 90°. Each primary and secondary pipeportions of the main and branch pipe sections have non-planar engagementsurfaces 306, 308 formed from two opposing portions 310, 312 whichpreferably intersect along a line that falls within a plane passingthrough the longitudinal axis L_(M) of the main pipe section 302. In thefabrication of such a fitting, the interior angle formed in the branchside of the heating assembly will also approximate 90° while theexterior angle formed on the opposite side of the heating assembly willbe approximately 270°.

In summary, it should be evident that the present invention offerssignificant advantages such as a more structurally sound weld iseffected between the primary and secondary pipes, a reduction in theamount of on-site fabrication of fittings and the like.

While the preferred embodiments of the invention have been shown anddescribed, it will be obvious to those skilled in the art that changesor modifications may be made therein without departing from the truespirit and scope of the invention.

We claim:
 1. A method of welding two double containment pipe sections together to form a double containment pipe fitting wherein one of said two pipe sections extends at angle away from the other pipe section, each pipe section comprising a primary pipe portion coaxially disposed within a secondary pipe portion, the primary and secondary pipe portions being separated from each other by an annular space therebetween, the method including the steps of: forming engagement surfaces in opposing portions of said primary and secondary pipe portions of said two pipe sections, positioning said two pipe sections in a spaced-apart relationship such that the longitudinal axis of one of said two pipe sections intersects the longitudinal axis of said other of said two pipe sections at a predetermined angle, said engagement surfaces of said one pipe section opposing said engagement surfaces of said other pipe section, simultaneously heating said primary and secondary pipe portion opposing engagement surfaces of said two pipe sections to a preselected welding temperature; and, moving said two pipe sections together such that said primary and secondary pipe portion opposing engagement surfaces are contacted together to thereby simultaneously join said primary and secondary pipe portions of said two pipe sections together.
 2. The method of claim 1, wherein said simultaneous heating step includes contacting said two pipe section engagement surfaces with a heating element having two opposite, non-planar heating surfaces defined thereon.
 3. The method of claim 2, wherein said one of said two heating surfaces has an interior angled portion and the other of said two heating surfaces has an exterior angled portion.
 4. The method of claim 2, wherein one of said two heating surfaces includes a male, contoured portion and the other of said two heating surfaces includes a female, contoured portion.
 5. The method of claim 4, wherein said one heating surface includes two male contoured portions, one of the two male contoured portions having an opening therein and the other of said male contoured portions being disposed within the opening and spaced apart from said one male contoured portion.
 6. The method of claim 5, wherein said the other of said two heating surfaces includes two female contoured portions, one of the two female contoured portions having an opening therein and the other of said female contoured portions being disposed within the opening and spaced apart from said one female contoured portion.
 7. The method of claim 4, wherein said the other of said two heating surfaces includes two female contoured portions, one of the two female contoured portions having an opening therein and the other of said female contoured portions being disposed within the opening and spaced apart from said one female contoured portion.
 8. The method of claim 2, wherein each of said heating element heating surfaces include respective distinct associated primary and secondary pipe contacting portions, which are spaced apart from each other.
 9. The method of claim 8, wherein the primary pipe contacting portion of one of said heating element heating surfaces protrudes past its associated secondary pipe contacting portion.
 10. The method of claim 2, wherein said simultaneous heating step includes contacting said two pipe section primary and secondary pipe portions with a heating element having opposing first and second heating surfaces defined thereon, each of said first and second heating surfaces having distinct, respective primary and secondary pipe-contacting surfaces, each of said first and second heating element primary pipe-contacting surfaces being disposed within said first and second heating element secondary pipe-contacting surfaces.
 11. The method of claim 10, wherein said heating element first heating surface primary pipe-contacting surface extends past said heating element first heating surface secondary pipe-contacting surface, and said heating element second heating surface secondary pipe-contacting surface projects past said heating element second heating surface primary pipe-contacting surface.
 12. The method of claim 1, further including the step of applying a preselected amount of pressure to said two pipe sections while moving said two pipe section engagement surfaces together.
 13. The method of claim 1, wherein said step of forming engagement surfaces in opposing portions of said two pipe section primary and secondary pipe portions includes the step of making openings in each of said primary and secondary pipe portions of one of said two pipe sections.
 14. A method of forming an angled, butt welded joint in thermoplastic coaxial pipe sections wherein said pipe sections include a header coaxial pipe section and a branch coaxial pipe section, the header and branch coaxial pipe sections each having inner pipes disposed within outer, surrounding pipes, the method comprising: forming first engagement surfaces on each of said header section inner and outer pipes, forming second engagement surfaces on each of said branch section inner and outer pipes, said first and second engagement surfaces of said header and branch section inner and outer pipes being generally complementary, aligning said header and branch pipe sections such that their inner and outer pipe first and second engagement surfaces oppose each other in a spaced-apart relationship, providing a heating element having two non-planar, opposing heating surfaces, simultaneously pressing said header and branch section inner and outer pipe opposing first and second engagement surfaces against the heating element non-planar opposing heating surfaces to soften the thermoplastic to a state suitable for forming a welded joint thereof, removing the heating element from contact with said header and branch pipe section inner and outer pipe opposing engagement surfaces and pressing said header and branch section inner and outer pipe opposing first and second engagement surfaces together under pressure until said thermoplastic material has cooled to a temperature below its softening point. 